Sea Level. John Church WCRP Antarctic Climate and Ecosystems CRC Centre for Australian Weather and Climate Research

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1 Sea Level John Church WCRP Antarctic Climate and Ecosystems CRC Centre for Australian Weather and Climate Research

2 Sea level rose by more than 120 m since the last glacial maximum 2 Church et al., 2008

3 Sea-level rise accelerated during the 20 th century Satellite altimetry Holgate and Woodworth, /- 0.3 mm/yr (1960 to 2000) Church et al., 2004,

4 Ocean thermal expansion a major contributor to sea-level rise Domingues et al

5 Glacier melting contributes to sea level Kaser et al

6 Ice mass loss of the Greenland ice sheet since 1992 Greenland contribution to present-day sea level rise ( ) : ~ 0.2 mm/year Ice mass change (Gt/year) Ice mass loss measured by remote sensing techniques Steffen et al. Cazenave,

7 The West Antarctic Ice Sheet is loosing mass (possible long-term loss) East Antarctic Zwally et al West Antarctic Contribution to present-day sea level rise ( ): ~0.2 mm/an Remote sensing measurements 7 (Cazenave, 2006)

8 Effect of global land water storage on global mean sea level Milly, P. C., D., A. Cazenave, and M. C. Gennero (Proc. Natl Acad. Sci, 2003) Ngo-duc T., K. Laval, J. Polcher, A. Lombard and A. Cazenave (GRL, 2005) greatest variation is associated with ground water, followed by soil moisture no significant trend was detected strong decadal variability driven by precipitation, strong decrease in the beginning of 1970s agreement between ORCHIDEE and LaD. (Land Dynamics LSM of GFDL) 8

9 Sum of contributions is close to the observed rise (but some remaining deficiencies and omissions) Domingues et al

10 The IPCC TAR and AR4 projections of sea-level rise are similar Larger values cannot be excluded IPCC 2001; IPCC 2007; Rahmstorf et al

11 How well are the IPCC projections Sea level rising near the upper limit of the IPCC TAR projections (i.e. 88 cm rise by 2100) standing up to the test of time? 11 Rahmstorf et al. 2007

12 Statistical models consistent with larger 21st C rise at/above upper end of IPCC range 12 Rahmstorf, 2006

13 What about the longer term? Sea-level rise continues long after stabilisation of concentrations Stabilisation of emissions will result in larger rates of change 13 Meehl et al., 2005

14 Uncertainties I Greenland Concern about icesheet stability and a substantially larger rise in sea level Paleo evidence for rates of SLR of 1 m/c in Eemian Surface melting For sustained warmings above 4.5±0.9 K in Greenland (3.1±0.8 K in global average), it is likely that the Greenland Ice Sheet would eventually be eliminated. [Gregory and Huybrechts, 2006] Dynamic instability Zwally et al. 2002, Das et al. 2008, Joughin et al

15 Uncertainties II Greenland and WAIS Loss of ice shelves Rapid propagation up the ice stream; Antarctic Peninsular and Greenland. Penetration of ocean water under the ice West Antarctic Ice Sheet and some outlet glaciers in Greenland. 15

16 Sea-level rise is expected to have regional variations Meehl et al

17 Response to changes is surface loading To understand regional sea-level rise need to allow for the earth s response to changes in surface loading (and other land motions) Mitrovica et al

18 The frequency of flooding events of a given magnitude has increased A 1 in 5 year event becomes a 1 in 2 year event. Church et al.,

19 Decrease in the return period of extreme events for a 0.1 m sea-level rise For a 0.5 m rise, a 1 in 100 year event could happen several times/year Hunter 2007; Church et al

20 Locations where the period between flooding events has decreased are shown in red. Top relative sea level Bottom relative to yearly average sea level 99 Percentile Trends since 1975 (Woodworth and Blackman, 2004 J. Climate) 20

21 Climate projections for TE2100 Improved storm surge projections: Ensembles Longer experiments Higher resolution What about the other IPCC AR4 models? Page 21

22 Ensemble projections of change in extreme sea levels Uncertainty in large scale atmospheric forcing Uncertainty in large scale patterns of time average sea level change Add in ice melt uncertainty Downscale to get uncertainty in Regional scale atmospheric forcing Run surge model simulations to estimate uncertainty range in local extreme water levels? Page 22

23 Based on data, unperturbed model Page 23

24 Do long time-slices provide an advantage? Page 24

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26 Requirements for improved projections Complete upper ocean observing systems Sustain observing systems in situ and satellite (Altimetry, gravity, SAR); data archeology, paleo data Deep ocean observations? More rigorous testing of ocean models reconcile existing differences Ice sheet and glacier contributions in situ and satellite observations, understanding and modelling; ice sheet stability Extremes high resolution data (space and time, length of series and models), waves and river flows, hurricane data sets, mid latitude storms, extend storm surge models, inundation and erosion Terrestrial storage, Geodetic reference frames, surface loading Small community with many contributions 26

27 Oil & Gas Industry and Sea Level Monitoring Philip Woodworth, Lesley Rickards and Thorkild Aarup Make all met ocean (esp. sea level) data acquired by the O&G industry available. Some data are accessible via the SIMORC project ( but it is not complete. O&G Industry could provide more access to offshore platforms for a range of operational oceanography; e.g. tide gauges and GPS for storm surge monitoring, satellite calibration or even tsunami warning. O&G Industry could host permanent GLOSS-standard coastal tide gauges at sites that it owns. Priority locations include W. Africa (e.g. Nigeria, Cote d Ivoire), Caribbean, S America, N Africa and Middle East. O&G Industry could support training of operators of GLOSS stations in developing countries, and support installations/maintenance to complete global networks. Support workshops extremes, sea level Encourage OGP Metocean Committee to send 27 representatives OGP/JCOMM/WCRP Climate to meetings Change and the of Offshore the GLOSS Industry Workshop, Programme. WMO, May 27-29, 2008

28 Report of the WCRP Workshop (163 participants, 29 nations) Thank you! 28

29 Sea levels currently rising at over 3 mm/yr 29

30 Regional patterns of Sea-level Rise Global Sea Level Trends: Nerem, 2005

31 Estimate sea-level by representing the variability using patterns determined from altimeter data Church and White,

32 Approach I Use satellite altimeter data to identify patterns of spatial variability Expand historical tide gauge data as a sum of these patterns; ie SSH r (x,y,t) = U r (x,y)α(t) Determine amplitudes of patterns by minimising difference between observed and reconstructed sea level Take account of error estimates and available information on spatial correlations; ie minimise S(α) = (HU r α SSH o ) T R -1 (HU r α SSH o ) + α T Λα 32

33 The distribution of available sea- level data changes with time Church and White,

34 Acceleration of Sea-level Rise The rate of rise for the last 20 years is 25% greater than any 20 year period over the preceding 110 years 34 Church and White 2006

35 Ocean temperatures control the regional patterns of sea-level Satellite sea- level trends Steric sea- level trends Domingues et al. in prep

36 Significant spatial variations in trends of sea level rise from 1950 to Church et al., 2004

37 ~hadto/extremes/r/trend_signif_rlargest_thames_ppt_slide_all_runids_with_trendy_50yr_rl.r What about the trends? Page 37

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40 New estimates of ocean heat content and ocean thermal expansion Domingues et al

41 The Science Shows: Ongoing sea-level rise is inevitable! It is an issue for Here and now, The 21 st C and The long term. Remaining gaps in ability to predict how much sea level will rise and changes in extreme events. Is it dangerous? At what level? For whom? Need to adapt Impacts felt through extreme events more frequent, more severe. LDCs and the poor most at risk. Require local and regional planning. Planning to avoid the impacts of severe events. Need to narrow uncertainties Need to mitigate to avoid the most extreme scenarios Without significant, urgent and sustained action, we could pass a threshold during the 21 st C, committing the world to metres of sea-level rise! Environmental refugees a here and now issue Not if but when, where and how will we respond? Essential and urgent that science/government/business/community 41 partnerships are strengthened!